It is not known to evolve into or from any other Pokémon, but it is considered to be a counterpart of Oranguru.
Passimian is a black-and-white Pokémon resembling a powerfully built lemur with broad shoulders. Most of its fur is white, but it has a black muzzle, upper body, hands, feet and ankles, and tail. However, there is a wavy white ring near the tip of its tail. The fur around Passimian’s head and face is longer and forms many small clumps, especially around the top of its head and under its chin. On top of its head is a pale green helmet similar to half of a coconut shell. The helmet has a small orange blaze on the front and two leaves that stand up straight attached to the back. Its eyes are partially hidden by its headwear, but its yellow sclerae and reddish-orange irises are visible. It is often seen carrying a large berry that resembles a green coconut. There are several leaves stuck on its body with saliva. The shoulders and chest all have one vertical and one horizontal leaf. While most Passimian have green leaves, the the anime has shown that there is a red leaf variant on Akala Island that has one additional horizontal leaf in each area. The leaves color and position are decided by the leader of a troop and aid in distinguishing one troop from another.
This Pokémon creates troops of 20 to 30 members. Each troop has a leader that picks 10 of the strongest members to search for food. This Pokémon’s battle strategy involves throwing Berries at opponents, hard ones for damage and soft ones to obscure vision, and confusing opponents by throwing the Berry to other troop members. A troop's leader is the member that can throw these Berries the farthest. Through rigorous training, the troop improves its coordination, teamwork, and skill in handling Berries. Some Passimian are unable to handle the intensity and flee from the troop. In place of a troop leader, a captive Passimian looks to its Trainer for leadership. If its Trainer has poor form when throwing Poké Balls, it will refuse to obey.
Multiple Passimian debuted in the banned episodeSM064, where they are revealed to have been organized in two groups. The members of one group have green markings and are from a forest behind Iki Town on Melemele Island, while the other group's members have red markings and are from Akala Island. Respectively, they are referred to as (Japanese: メレメレグリーンズMelemele Greens) with their leader being nicknamed (Japanese: タイニーTiny), and (Japanese: レッドバンズRed Buns) with their leader being nicknamed (Japanese: かぎづめKagizume). As the episode only aired in Asia, they don't have English names.
Passimian can be seen as a counterpart to Oranguru. Both are primate Pokémon with the same base stat total. While Passimian is exclusive to Pokémon Sun and Pokémon Ultra Sun, Oranguru is exclusive to Pokémon Moon and Pokémon Ultra Moon.
Passimian appears to be based on a lemur, with a striking resemblance to the black-and-white ruffed lemur. Lemurs also live in large groups and are very cooperative in activities like searching for food, like Passimian. It may also draw inspiration from quarterbacks in American football.
Passimian may be a combination of pass and simian. It may also be a play on prosimian.
Nagetukesaru may be a combination of 投げつける nagetsukeru (to throw) and 猿 saru (monkey).